This invention generally relates to gamma-ray lasers and more particularly relates to Mossbauer effect gamma-ray lasers. This invention is the result of a contract with the Department of Energy (Contract No. W-7405-ENG-36).
The development of sources of coherent radiation has progressed steadily toward shorter wavelengths. Current devices make use of high energy transitions in atoms for photon generation in the wavelength range down to about 50 .ANG.. The development of lasers that would generate radiation at still shorter wavelengths, comparable to atomic dimensions, would greatly extend the applications of lasers. The development of a gamma-ray laser (graser) would combine the characteristics of gamma-ray radiation (i.e., penetration, ionizing ability, short wavelength, interaction with electrons in inner shells of atoms and with nuclei) with the properties of radiation generated by stimulated emissions (coherence, intensity, monochromaticity, directionality, time and frequency dependence, etc.).
A review of various approaches to gamma-ray laser development is found in G. C. Baldwin et al., "Approaches to the Development of Gamma-Ray Lasers," 53 Rev. Mod. Phy., No. 4, Part I, pp. 687-744, incorporated herein by reference. A nuclear transition is required with an intermediate lifetime in at least the nanosecond range, with transition energies in the 6- to 120-keV energy range in order to yield coherent radiation in the wavelength range between 0.1 to 2 .ANG.. A substantial portion of the literature is particularly directed to the application of recoilless emission and absorption (Mossbauer effect) to enhance the stimulated emission probability.
For previously proposed concepts requiring recoilless emission and absorption, the intensity of radiation necessary for creating the required inversion density is so intense that the laser would be vaporized before the conditions can be established to obtain lasing action. The pumping radiation can be reduced if the nucleus is transmuted to a second species in the pumping process, but the required radiation is still too intense to obtain the necessary state population inversion for lasing. To further reduce the required pumping intensity it has been suggested to physically separate the pumping and the lasing process. For intermediate lifetime isomers, separation schemes are suggested by Baldwin et al., page 706. For a short lifetime isomer, Baldwin et al., page 706, discuss a cylinder filled with Kr and having a center wire of beryllium. On ionization, the excited Kr would be drawn by an electric field to the Be wire and implanted in the Be for subsequent Mossbauer radiation.
Thus, it has been suggested that excited isomers be separated from unexcited isomers and then implanted in a host material, such as Be, that can bind the atoms with sufficient strength in the lattice to establish the required Mossbauer conditions. The separation and implantation must be accomplished, however, in a time small compared to the halflife of the transition. Since Mossbauer conditions have not been observed for nuclei with halflives greater than about 10.sup.-6 seconds, these manipulations must occur very rapidly.
In accordance with the present invention, a gamma-ray laser configuration provides for the separation and implantation of an excited isomer in a time small compared to the transition halflife. The radiation pumping requirements are reduced to intensities which do not disturb the integrity of the material establishing the Mossbauer conditions.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.